1. Field of the Invention
The invention relates to frequency modulated, continuous wave radar systems, and more specifically to linear frequency sweep circuits for use in such radar systems.
2. Description of the Prior Art
Frequency modulated continuous wave (FMCW) radar systems require a source of linear periodic frequency sweep signals in order to achieve range resolution.
Typically the sweep circuits in such systems employ a voltage controlled oscillator (VCO) which is frequency turned by means of a drive voltage. Ordinarily the drive voltage is used to bias the VCO itself or to actuate a varactor diode installed in a microwave cavity associated with the VCO.
With either of the aforementioned tuning methods, the output frequency is a non-linear function of the drive voltage. Thus in order to provide a linear frequency sweep a non-linear drive compensation circuit or linearizer must be utilized. Typically, such linearizers comprise compensation means with as many as 15 adjustment potentiometers which are individually adjusted by a trial and error alignment procedure. In many instances, such compensation means are temperature sensitive so that the VCO had to be temperature-regulated. Furthermore since such linearization means are essentially open loop circuits, the compensation had to be continually re-adjusted to offset the effects of changing VCO or linearizer circuit properties, operating conditions, age and handling.
The present invention overcomes these shortcomings by employing a novel feedback system to overcome the effects of changing circuit parameters and operating environment.